Leading military and diplomatic figures from the U.S.-led coalition fighting the Islamic State (IS) extremist group met on July 21 to prepare for a major assault on the militants' Iraqi stronghold of Mosul.

Defense and foreign ministers from more than 40 countries met in Washington for a second day to discuss the impending operation to take Mosul, Iraq's second largest city and IS's most important stronghold in that country.

"The liberation of Mosul is now in sight," said Brett McGurk, the United States' envoy to the coalition.

Iraqi Prime Minister Haidar al-Abadi has pledged to retake Mosul by the end of the year.

U.S. Secretary of State John Kerry said that in less than two years the coalition had driven the militants from nearly half its territory in Iraq and 20 percent of its territory in Syria.

"Today, we can look forward without exaggeration, to a time when [IS] is driven completely out of Iraq and Syria," Kerry said.

The operation to take Mosul, an ethnically diverse city of 1 million, is expected to be difficult.

There have been disagreements between Iraq's Shi'ite-dominated government, Sunni leaders, and Iraq's autonomous Kurdish region over how post-war Mosul will be rebuilt and governed.

There has been agreement, however, that 15,000 locally recruited troops from the region will be involved.

"Mosul will be the most complex operation to date," McGurk said, although he added that the plan is "well underway.”

"The liberation of Mosul… is now an achievable objective and it's one we must get right," he said.

On the first day of the talks, the defense ministers met to talk battlefield tactics, while the foreign ministers pledged $2 billion in reconstruction funds.

The UN said it needs to raise $284 million in aid to prepare for humanitarian needs from an expected assault on Mosul, and an additional $1.8 billion would be needed to deal with the aftermath.